When activated, Kupffer cells (KCs), the fixed tissue macrophages of the liver, release mediators such as reactive oxygen species, cytokines and proteolytic enzymes that could contribute to hepatocellular damage. The possibility that stimulation of KCs plays a role in chemical-induced liver injury has not been explored as a general mechanism of toxicity. The proposed research will address the hypothesis that activated KCs contribute to hepatotoxicity caused by some toxicants and will explore mechanisms by which this may occur. Studies will focus on allyl alcohol (AA) because preliminary evidence suggests that AA activates KCs and that KCs play a role in AA-induced hepatotoxicity. Initial studies to investigate the hypothesis that KCs contribute to AA-induced hepatotoxicity will be conducted to evaluate the time course of activation of KCs and the development of hepatocellular injury in AA-treated rats in vivo to determine the temporal relation between KC activation and toxicity. In addition, KC activity will be enhanced or inhibited in AA-treated rats to determine whether modulation of KC activity alters AAinduced hepatotoxicity. Furthermore, the ability of KCs to potentiate AA-induced toxicity to isolated hepatic parenchymal cells will be examined. A parallel series of experiments will be conducted with an active metabolite of AA, acrolein, to establish the role of this metabolite in KC-dependent injury to parenchymal cells. Experiments will be performed to determine whether the mechanism by which KCs enhance AA-induced toxicity involves KC-derived mediators. The possible involvement of reactive oxygen species, lysosomal enzymes, tumor necrosis factor, and metabolites of L-arginine will be examined. Finally, studies are proposed to determine whether the periportal nature of toxicity due to AA can be explained by differences in KC function in periportal and pericentral regions of the liver lobule. An overall goal of this research is to study mechanisms by which activated KCs may contribute to hepatotoxicity. The proposed experiments focus on AA, but the ultimate intent is to extend these studies to other hepatotoxicants. The results should provide understanding of the mechanisms by which activated KCs contribute to liver toxicity.